This invention relation to a system for progressively placing the roof structure in place as the tunnel is being bored with a tunnel boring machine (TBM). This invention will be found to be most effectively used on open or main beam type TBM""s in situations where a tunnel is being bored in a rock strata wherein the roof is somewhat unstable.
When boring a tunnel in subterranean rock, the TBM""s of the present invention utilize a rotating boring head to spall and crush a rockface by exerting pressure on the rockface by means of a series of cutting elements mounted on a rotating boring head.
As the rockface is gradually eroded, the forward portion of the TBM on which the boring wheel is mounted moves ahead while thrusting against a gripper system which is wedged into the previously formed tunnel. The thrust system provides the required force to crush the rock at the rockface.
Because some tunnels must be driven into rock which is unstable or becomes unstable when subjected to the forces exerted on the rockface by the excavation, it is not unusual to have fractures in the strata surrounding the tunnel itself. These fractures produce discrete pieces of rock which can fall into the tunnel opening if they are not held in place after the TBM moves forward.
If the fractures occur in the bottom or sides of the tunnel, it is of little consequence. However, if the strata through which the tunnel is being bored is of the right type and consistency, rock fractures occurring in the tunnel roof may allow portions of the roof to fall which can have serious consequences for the tunneling operation. Falling rock from the tunnel roof may endanger tunnel workers and the tunneling machinery but the falling rock creates an uncontrolled opening above the tunnel and generally disrupts the excavation process.
Some TBM""s have employed a shield in the form of a partial cylinder which fits close to the most recently formed tunnel roof just behind the boring head of the TBM. The shield is sometimes provided with some means or other to move the shield vertically so as to be able to engage or remain clear of the tunnel roof. The shield provides the protective structure to prevent falling rock from injuring TBM operating personnel but does not provide a permanent support for the tunnel roof. As the shield moves forward with the TBM, it uncovers the tunnel roof which if not otherwise supported, can fall.
It is not unusual to encounter conditions where falling rock from the roof of a newly formed tunnel can present such a hazardous situation that the boring operation must be halted while a temporary roof is placed in the newly formed tunnel. Arc shaped cylindrical segments of a suitable material (usually steel) may be bolted to the roof by rock bolts. If the TBM shield has a fingered shield which will permit the installation of rock bolts between the shield fingers, metallic roof ribs may be fastened to the roof of the tunnel while the shield is yet above the rib. Of course, the exposed ends of the rock bolts which protrude between the fingers of the TBM shield may present a problem if for some reason the fingers of the TBM shield move laterally, as may well happen during a steering correction operation of the TBM. Rib systems placed with finger shields, though providing support for the tunnel roof at periodic spaced intervals, has the shortcoming of not providing support for the tunnel roof between the placed ribs. Because of the shape of the shield and its extending fingers, a large proportion of the tunnel roof is obscured by the extending fingers and if an attempt is made to install timbers etc. between the fingers of the shield, the previously installed rock bolts prevent the insertion of such roof support members between the extending shield fingers.
At times wire mesh (similar to chain link fence or concrete reinforcing mesh) has been used between the roof ribs and the fingers of the shield to prevent rock fall from the exposed portion of the tunnel roof between the shield and the roof rib, but this method of support suffers from the lack of rigidity of the mesh between the shield and the last installed rib. The mesh tends to sag as rock drops from the roof; this sagging mesh not only protrudes into the tunnel destroying the tunnel profile, but serious deterioration of the roof may occur above the mesh.
Before applicants"" instant invention, the only effective method previously known for the installation of longitudinally extending support members between the roof ribs was to install such members after the finger shield had moved onward away from the ribs and exposed the whole roof.
However, if loose roof rock is present above the finger shield, it will usually fall before or during installation of the longitudinal support members. The potential for falling rock endangers personnel and hinders the construction process.
When boring through other types of strata, problems relating to falling debris from the roof of the tunnel may occur due to the disturbance caused by the TBM""s boring activity and this invention may be efficiently employed to provide a safe environment for the tunneling personnel who must perform operations in the tunnel to bring the tunnel construction to completion.
The TBM of this invention is provided with a shield which comprises a series of hollow rectangular tubes arranged in an arc (akin to slats in a lobster trap) which are fastened together and mounted on a framework of curved beams so as to extend longitudinally along the tunnel axis and have substantially the same surface curvature as the tunnel roof. The tubes extend from a point immediately behind the TBM boring head to a point where the support of the tunnel roof is completed.
The framework is attached to the TBM in such a manner that the curved upper surface formed by the tubes forming the shield may be held against the tunnel roof. The height of the shield is adjustable within predetermined limits.
The tubes forming the shield are of a length required to extend from a point just behind the cutter head to a support installation point and are of such size as to accommodate the elongated members which will provide the primary tunnel roof lining. Thus, the xe2x80x9cshieldxe2x80x9d comprising a plurality of hollow tubes is xe2x80x9cloadedxe2x80x9d preferably with timber members, such that the ends of the timber pieces protrude from the hollow tubes behind the shield so that they may be fastened by some means or other to the tunnel roof. The tubes are intentionally made to be somewhat larger in cross section than the timber lagging members which are inserted inside the tubes so that the lagging timbers enjoy a xe2x80x9csloppyxe2x80x9d fit.
As the boring machine moves into the rock, more of the timber members are exposed almost as if in an extrusion operation. Metallic or other curved or ring support beams may be subsequently installed by the tunnel building personnel as the machine moves away from the last installed roof beam.
The ends of the timber lagging members are intentionally staggered lengthwise along the tunnel roof, so that at no time does a pair of coincident joints occur in adjacent rows at the lagging members. Each time a tube is emptied of its lagging timber, a new lagging timber is pushed into the empty tube to be subsequently fed out as the TBM advances. This causes staggered laps in the timber lagging members forming the completed roof.
This patent describes a TBM having a shield comprising a series of xe2x80x9cTxe2x80x9d shaped members mounted on a curved beam structure. Lagging members are installed between the T shaped members such as 58, 59 and the supporting beams such as 30 and 31.
The lagging members (17, 48, etc.) are installed in the space between support beams 30, 31 and the T shaped members of the shield by lowering the support beams 30, 31 by means of cylinder actuators 36, 37 to provide the necessary space to insert lagging members 17, 48, etc.
TBM""s must be stopped at intervals to permit the xe2x80x9cminedxe2x80x9d material produced by the boring head to be removed, and it is during this time that the support beams 31, 32 may be lowered to permit the insertion of new lagging members 17, 48, etc. in the space between T members 17, 48, etc. and support beams 30, 31.
If, however, the TBM has moved a sufficient distance that a substantial portion of the tunnel roof has not been lagged due to the progress made in the boring operation, it may be necessary to halt the boring operation to install the lagging members in the shield.
Additionally, once the lagging members 17, 48, etc. have been installed in between the T shaped shield members 58, 59; 60, 61; etc., there is little opportunity to install rock bolts between the T shaped shield members.
After the shield has left the lagging members 17, 48, etc. exposed a support system must be installed to hold the lagging members against the roof.
The patent describes the use of ring beams 23, 24, etc. which are subsequently installed, and wedges such as 79 are used to xe2x80x9cjackxe2x80x9d the lagging members against the tunnel roof.
Other methods of securing the lagging members 17, 48, etc. to the roof i.e. rock bolts are discussed in the patent but these are almost impossible to install while the TBM shield is between the lagging members and the tunnel roof.
Lastly, the above U.S. Patent makes no suggestion of staggering the joints in the lagging members; all the lagging members have been purposely manufactured to have the same length so as to be supported at each end by ring supports 23, 24, etc.